Stators for a linear stepper motor are needed in large numbers so that even minor savings in the manufacturing process have a significant economic impact. There are therefore a large number of different stator designs. Generally, they have ball bearing or plain bearing seats for radial support and for dissipating the radial forces from the rotors. There is a requirement for these stators of linear stepper motors to be able to position an actuating rod as precisely as possible both radially and axially, i.e. specifically the axial play of the spindle relative to the spindle nut and the axial play of the whole spindle in the housing should be as small as possible. Most stators are made from a large number of components, resulting in high overall costs, not least because of long assembly times or labour-intensive operations. With many individual components, the variety of components creates a long dimensional chain which may lead to inaccuracies due to the admissible tolerances of the individual components. For these reasons the air gap between the stator and the rotor is often chosen larger so that the accuracy of the actuating force or the efficiency of the linear stepper drive is reduced.
A generic linear stepper motor is known from DE 103 32 389 A1, where the outer web ends of the actuating rod of this linear drive are of such a length that they can be fitted through corresponding guide cut-outs of the D-side bearing shield. After fitting through, a coupling shank that closes the web ends of the actuating rod is fitted and suitably fixed. The stator is bounded by two bearing shields, where two plain bearings for radial support and two balls for axial support of the spindle are arranged in both bearing shields by means of plain bearing journals of appropriate length. A problem here is the wobbling movement of the bell-shaped rotor induced by the two plain bearings and the precise adjustment of axial play.
According to EP 1 414 636 B1, an electro-mechanical linear drive with electric motor, having a hollow shaft rotor, open at one side, and a spindle shaft in the interior of the hollow shaft rotor, a helical gear converting the rotational movement of the hollow shaft rotor into a linear movement, wherein the rod-shaped end of a sleeve-shaped spindle nut protrudes from the open D-side of the linear drive. The hollow shaft rotor itself is cantilevered in the stator on the D-side of the linear drive and the stator consists of a relatively large number of components.
EP 1 928 074 B1 describes a linear actuator comprising a common motor design in a separate two-piece housing with internal rotor with rotor shaft, a stator with coil, the rotor being radially and axially supported by a bearing on the motor side. Directly following the rotor shaft a threaded shank is formed on which a screw-nut system is arranged for producing a linear movement. This linear displacement unit is designed as a fork shape and consists of a nut portion and a coupling portion for its connection with a unit to be controlled. Furthermore, the motor shaft is axially supported by two balls, the balls bearing against hard stops. Moreover, this design additionally has a spring arranged in a bearing intended to prevent axial play of the rotor shaft with the following spindle. This design is characterised by a large number of components and has a relatively long structure.
Another linear drive with a claw-pole stepper motor is shown in DE 10 2008 054 330 A1, where the motor housing is also a radially split two-piece design. After assembly of the motor components, both motor housing halves can be locked and positioned against each other by means of bayonet joint. In this drive solution, too, the linear motor consists of an elevated number of components. To provide radial support, two radial grooved ball bearings are internally arranged.
DE 10 2005 055 868 B1 describes another threaded drive for a linear servo-motor with a flanged two-piece housing, designed as a very short structure, since the threaded spindle is supported and guided by two ball bearings inside the linear servo-motor. However, this motor also consists of a relatively large number of components, which makes its manufacture unnecessarily costly.
The present disclosure is based on the task to create a novel stator for a linear stepper motor, which is built of few components and which can be manufactured economically in an automated manner.